Method for producing sheet metal part and a forming tool

ABSTRACT

In a method for producing a sheet metal part, a sheet metal blank is rolled to have at least two regions of different material thickness to define a thick region and a thin region, with a thickness profile of the sheet metal blank extending in substantial symmetric relationship to a central plane of the sheet metal blank. The sheet metal blank is inserted into a forming tool having a punch and a die and a punch-proximal side of the sheet metal blank is contacted with a pressing cam formed on the punch. The sheet metal blank is formed into the sheet metal part by pressing the punch against the die and thereby forming an embossment by a die cam provided on the die on a die-proximal side of the sheet metal part.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the priority of German Patent Application Serial No. 10 2011 009 890.9, filed Jan. 31, 2011, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a method for producing a sheet metal part and a forming tool for forming a rolled down sheet metal blank.

The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.

Metal parts are often used in the automobile industry. By varying the wall thickness profile of the structural part, loads can be better distributed across the structural part and optimized crash behavior can be realized. As starting material for such parts, blanks are used which for example are reinforced with additional patches or made of multiple individual parts which are welded to one another.

U.S. Pat. No. 3,896,653 discloses a method to produce blanks with variable thicknesses by changing the distance between two rollers during a rolling process to achieve a defined change in thickness of the metal. Such a process is known for example from DE 22 45 650 A1.

Typically, the change of thickness extends symmetric to a central plane of the metal strip or the metal blank. The distance of the central plane to the top and bottom side is thus always the same in the observed surface area. The variation in thickness then results from varying the distance, wherein the distance of the central plane to the top side and bottom side always varies in the same manner. In the case of a sheet metal blank with two different sheet thicknesses, a thickness step is thus created between the two regions of different sheet thickness. The presence of such a thickness step is disadvantageous in particular with regard to coupling processes, for example thermal joining or bonding, because the parts to be coupled must either have a surface geometry which corresponds to the thickness step on one side, or the thickness step must be compensated by increased adding of welding filler materials or adhesives. This however, leads to inadequate coupling in these regions. In the case of bonding, the strength of the bonding connection is compromised as a result of excessive adhesive or adhesive which has been applied too thick. In the case of welding, the addition of welding filler material for compensating the thickness step leads to an increased heat input and thus to a change in strength in this region.

Especially with regard to the formation of selectively deformable or stiff regions in structural parts of motor vehicles, for example motor vehicle pillars or vehicle doors or the like, it is important to attain high production accuracy while at the same time to allow adjustment of desired product properties.

It would therefore be desirable and advantageous to obviate prior art shortcomings and to provide an improved method to form sheet metal blanks with high precision, and to provide an improved forming tool that enables a forming of rolled sheet metal blanks with ease and compensation of possible tolerances of the sheet metal blank.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a method for producing a sheet metal part includes rolling a sheet metal blank to have at least two regions of different material thickness to define a thick region and a thin region, with a thickness profile of the sheet metal blank extending in substantial symmetric relationship to a central plane of the sheet metal blank, inserting the sheet metal blank into a forming tool having a punch and a die, contacting a punch-proximal side of the sheet metal blank with a pressing cam formed on the punch, and forming the sheet metal blank into a sheet metal part by pressing the punch against the die and thereby forming an embossment by a die cam provided on the die on a die-proximal side of the sheet metal part.

With the method according to the invention, it is possible to compensate possible part tolerances of a rolled sheet metal blank, when inserting the sheet metal blank into the tool, by using cams. A rolled sheet metal blank substantially includes at least two regions of different thicknesses, wherein a thick region has a higher material thickness relative to a thin region. The two regions are connected to one another by a transitional region. Such a transitional region can be only a few millimeters wide, however, it can also be up to several hundred millimeters wide. The decrease in thickness in the transitional region in this case may be only 0.5 mm, however, it can also be up to several millimeters.

When sheet metal blanks have defects caused during rolling, or when sheet metal blanks are inserted incorrectly, the provision of at least one pressing cam causes the sheet metal blank to be pressed against the die and, upon further closing of the forming tool, the sheet metal blank is pressed against the second half of the forming tool. As a result, the sheet metal blank is clamped by the cam and at the same time a minimal embossment is formed.

Advantageously, hollow spaces are provided opposite the cams so that compensation or shifting of the sheet metal part is possible when being inserted in the forming tool. The hollow space also allows for compensating thickness errors especially when the sheet metal blank is thicker in the region of the cam than expected. The sheet metal blank in connection with the cam follows hereby the principle of a chain tensioner, whereby a complete closing of the forming tool is realized. A particular advantage of the method according to the present invention is that in the case of cold forming, a controlled forming takes place in the region of the cam without the occurrence of an undefined wave formation. In the case of hot forming on the other hand, an at least one sided contact with the tool is always given, such that the cooling required for press hardening is ensured.

The punch is pressed against the die so that the sheet metal blank, located in between the punch and the die, is formed into the desired part, wherein a die cam formed on the die, forms an embossment on the die-proximal side of the sheet metal part. Thus two cams are formed, i.e. a pressing cam and a die cam, causing a double clamping of the metal sheet when closing the forming tool. As a result, an S-shaped or Z-shaped clamping region is formed which ensures that no uncontrolled wave formation occurs and that possible part tolerances or thickness tolerances respectively, are compensated.

According to another advantageous feature of the present invention, the sheet metal part can have a section which extends from the die cam in a direction of an edge of the sheet metal part and is in complete contact with the die in a closed state of the forming tool, with the punch-proximal side of the sheet metal part having opposite to the section a hollow space formed at least in an area between the punch and the punch-proximal side of the sheet metal part. The same advantages are hereby attained as described above and overall operating costs are kept to a minimum while producing sheet metal parts with high precision.

According to another advantageous feature of the present invention, the method is executed by a hot forming tool.

According to another advantageous feature of the present invention, the formed sheet metal part can be press hardened in the forming tool by quenching. Quenching can be carried out during the forming but also after completion of the forming. A sheet metal blank heated above AC₃ temperature can be hot formed and press-hardened in the forming tool. Sheet metal parts of high accuracy can be produced with high strength rates, and at the same time homogenous hardening of the sheet metal part, while using only small forming forces. As contact to at least one side of the forming tool is ensured, optimal heat dissipation during quenching can be established so that cycle times can be reduced during production of the sheet metal parts, while at least maintaining or increasing product quality.

According to another advantageous feature of the present invention, when forming the sheet metal blank into the sheet metal part, a waveform can be formed on the sheet metal part in a cross sectional direction of the sheet metal part as a result of an offset of the die cam relative to the pressing cam. This waveform can be S-shaped, Z-shaped or formed similar to the hybrid form. Both cams are offset in the plane of the sheet metal on the tool itself. Thus, via the offset, an embossment is formed on the punch-proximal side and die-proximal side of the sheet metal part to be produced through the forming process. The cross sectional course at this embossment offset itself has a wave-shaped, in particular Z- or S-shaped geometry. Again, a principle of a spring tensioner is applied here.

According to another advantageous feature of the present invention, a first embossment can be formed on the die-proximal side of the sheet metal part and a second embossment can be formed on the punch-proximal side of the sheet metal part, wherein the first and second embossments have an embossment offset relative to one another as a result of the offset of the die cam relative to the pressing cam. relative to one another as a result of the offset of the die cam relative to the pressing cam.

According to another advantageous feature of the present invention, the sheet metal blanks can have a material thickness between 0.5 mm and 5 mm, in particular 0.8 mm to 3.5 mm. Currently preferred is a material thickness between 1.2 mm to 2.2 mm.

According to another advantageous feature of the present invention, the rolling step can be executed to realize a rolling reduction of the sheet metal blank of maximally 50% of a material thickness of the sheet metal blank. The subsequent forming step optimally compensates product tolerances occurring during rolling in combination with the afore-mentioned sheet thicknesses.

According to another advantageous feature of the present invention, the embossment can have a cross sectional width of at least 0.75 times a thickness of the thin region. Suitably, there is no significant change of the sheet thickness during forming.

According to another advantageous feature of the present invention, the sheet metal part can be joined to another part by a material joint, a force fit and/or formfit. For example, a welding process or a bonding process and/or a clinching can be applied. The method according to the invention is particularly suited to produce joining surfaces with particularly high accuracy for the subsequent joining operation. In particular, the sides of the sheet metal part, which are important for the subsequent joining operation, are precisely produced with the method according to the invention.

According to another advantageous feature of the present invention, the die cam and/or pressing cam can be positioned such that the first and second

According to another aspect of the present invention, a forming tool for forming of a rolled sheet metal blank into a sheet metal part includes a punch, and a die, wherein at least one member selected from the group consisting of the punch and the die has a cam disposed in a transitional thickness region of the rolled sheet metal blank, and wherein in a closed state of the forming tool, a hollow space is formed at least in an area on a side opposite the cam between the sheet metal part and the member.

In accordance with the present invention, rolled sheet metal blanks can be processed with the forming tool such that a complete closing of the forming tool is always given while using only small forming forces. The sheet metal blanks have a thick region and a thin region, wherein the thick region and the thin region are coupled to one another by a transitional thickness region. The at least one hollow space provided on the side opposite the cam, allows for compensation in case of a shifting when inserting the metal sheet in the forming tool. Compensation of production tolerances of the sheet thickness of the rolled sheet metal is also possible. The size and the length of the hollow space can be configured according to the expected insertion tolerances and/or production tolerances.

According to another advantageous feature of the present invention, the cam can be formed over a complete half of the tool at least in regions, and a hollow space is only present on the side opposite the cam when the sheet metal blank is inserted and the forming tool is closed. For example, the entire punch can be formed in the shape of a cam so that a hollow space essentially extends over a large region of the die and thus at least a one-sided contact of the sheet metal blank is ensured. As a result of the one-sided complete contact, the sheet metal blank or the produced sheet metal part possesses on this side a correspondingly high accuracy with regard to the produced part geometry.

According to another advantageous feature of the present invention, the transitional thickness region can extend between a thick region and a thin region of the sheet metal blank, with the cam having a thickness which essentially corresponds to a thickness of the thick region less a thickness of the transitional region at a position of the cam. This ensures that a corresponding clamping is created by the cams and a correspondingly precise sheet metal part is formed.

According to another advantageous feature of the present invention, the forming tool can be constructed in the form of a hot forming tool for hot forming and press hardening.

BRIEF DESCRIPTION OF THE DRAWING

Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:

FIG. 1 is a sectional view of one embodiment of a forming tool according to the present invention; and

FIG. 2 is a sectional view of another embodiment of a forming tool according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the drawings are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.

Turning now to the drawing, and in particular to FIG. 1, there is shown a sectional view of one embodiment of a forming tool according to the present invention, generally designated by reference numeral 1 for forming a rolled sheet metal blank 2 into a sheet metal part 2′. The sheet metal blank 2 has a thick region 3, a thin region 4 and a transitional region 5 connecting the thick region 3 and the thin region 4. The wall thickness W3 of the thick region 3 is thus greater than the wall thickness W4 of the thin region 4. The wall thickness W5 of the transitional region 5 decreases from the wall thickness W3 of the thick region 3 to the wall thickness W4 of the thin region 4. The decrease can be progressive, degressive or linear.

The forming tool 1 has a punch 6 and a die 7, which form a hollow space 8 in-between. A pressing cam 9 is formed on the punch 6 and a die cam 10 is formed on the die 7. An offset 11 is formed in the sheet metal plane E between the pressing cam 9 and the die cam 10. The opposing region 12 of the pressing cam 9 or the die cam, respectively, is characterized by a hollow space 13, in which the rolled sheet metal blank 2 contacts the die 7 and/or punch 6 with the die-proximal side 14 and/or punch-proximal side 15. As a result of the forming operation, an embossment 16 is formed on the part by the pressing cam 9 and the die cam 10. The embossment 16 on the punch-proximal side 15 has an embossment offset 17 relative to the embossment 16 on the die-proximal side 14, which is generated by the offset 11 of both cams 9, 10 relative to one another.

FIG. 2 is a sectional view of another embodiment of a forming tool 1 according to the present invention. In this embodiment, the entire punch 6 at least in regions is formed as cam, and a hollow space 8 is formed on the side opposite the die 14 between the die 14 and the sheet metal part 2′.

While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: 

1. A method for producing a sheet metal part, comprising: rolling a sheet metal blank to have at least two regions of different material thickness to define a thick region and a thin region, with a thickness profile of the sheet metal blank extending in substantial symmetric relationship to a central plane of the sheet metal blank; inserting the sheet metal blank into a forming tool having a punch and a die; contacting a punch-proximal side of the sheet metal blank with a pressing cam formed on the punch; and forming the sheet metal blank into a sheet metal part by pressing the punch against the die and thereby forming an embossment by a die cam provided on the die on a die-proximal side of the sheet metal part.
 2. The method of claim 1, wherein the sheet metal part has a section which extends from the pressing cam in a direction of an edge of the sheet metal part and is in complete contact with the punch in a closed state of the forming tool, with the die having opposite to the section a hollow space formed at least in an area between the die and the die-proximal side of the sheet metal part.
 3. The method of claim 1, wherein the sheet metal part has a section which extends from the die cam in a direction of an edge of the sheet metal part and is in complete contact with the die in a closed state of the forming tool, with the punch-proximal side of the sheet metal part having opposite to the section a hollow space formed at least in an area between the punch and the punch-proximal side of the sheet metal part.
 4. The method of claim 1, wherein the forming step is executed by a hot forming tool.
 5. The method of claim 4, wherein the formed sheet metal part is press hardened in the forming tool by quenching.
 6. The method of claim 1, wherein when forming the sheet metal blank into the sheet metal part, a waveform is formed on the sheet metal part in a cross sectional direction of the sheet metal part as a result of an offset of the die cam relative to the pressing cam.
 7. The method of claim 1, wherein a first embossment is formed on the die-proximal side of the sheet metal part and a second embossment is formed on the punch-proximal side of the sheet metal part, and wherein the first and second embossments have an embossment offset relative to one another as a result of the offset of the die cam relative to the pressing cam.
 8. The method of claim 1, wherein the sheet metal blank has a material thickness between 0.5 mm and 5 mm.
 9. The method of claim 1, wherein the sheet metal blank has a material thickness between 0.8 mm and 3.5 mm.
 10. The method of claim 1, wherein the sheet metal blank has a material thickness between 1.2 mm and 2.2 mm.
 11. The method of claim 1, wherein the rolling step is executed to realize a rolling reduction of the sheet metal blank of maximally 50% of a material thickness of the sheet metal blank.
 12. The method of claim 1, wherein the embossment has a cross sectional width of at least 0.75 times a thickness of the thin region.
 13. The method of claim 1, further comprising joining the sheet metal part to another part by a joining process selected from the group consisting of material joint, force fit, and formfit.
 14. The method of claim 7, wherein the die cam and/or pressing cam is positioned such that the first and second embossments are formed in a region of the sheet metal part which is not used for joining.
 15. A forming tool for forming of a rolled sheet metal blank into a sheet metal part, comprising a punch; and a die, wherein at least one member selected from the group consisting the punch and the die has a cam disposed in a transitional thickness region of the rolled sheet metal blank, and wherein in a closed state of the forming tool, a hollow space is formed at least in an area on a side opposite the cam between the sheet metal part and the member.
 16. The forming tool of claim 15, wherein the transitional thickness region extends between a thick region and a thin region of the sheet metal blank, said cam having a thickness which essentially corresponds to a thickness of the thick region less a thickness of the transitional region at a position of the cam.
 17. The forming tool according to claim 15, constructed as a hot forming tool. 